1. Field of the Invention
This invention relates to a display method utilizing the thermally induced color change of a film made of a diacetylene derivative compound.
2. Description of the Related Art
It is hitherto known that films formed by coating and drying a solution of a diacetylene derivative compound on a carrier have the following properties.
(1) The film is colorless in its original state and, when irradiated by ultraviolet rays to cause a certain degree of polymerization, it will transform into a first state giving a blue color. This first state of blue color is stable and can not return to the original colorless state even after the irradiation of the ultraviolet ray has been discontinued. The change from the original state to the first state caused by a ultraviolet ray is irreversible.
(2) The film in the first state, when heated to about 50.degree. C. by imparting a thermal energy, will transform into a second state of red color. This second state of the film cannot return to the first state of blue color even after the heating is stopped and the film is cooled. The change from the first state to the second state due to a heat is also irreversible.
(3) The film in the second state, when heated further to about 300.degree. C. by imparting a thermal energy will transform into a third state of yellow color. This third state of the film can return to the second state when the heating is stopped and the film has been cooled. Thus the change between second state and third state is reversible.
Extensive researches are being made to develope a fixed display (i.e., a hard copy) by utilizing the irreversible change between the first and the second state and to develop an erasable display (i.e., a soft copy) by utilizing the reversible change between the second state and the third state on the basis of the abovementioned property of the diacetylene derivative films.
In preparation of a soft copy utilizing the thermally induced reversible change between the second state and the third state of a diacetylene derivative film, a large amount of thermal energy is required for display because a high temperature of about 300.degree. C. is required for the change from the second state to the third state. Moreover, with a less intense thermal energy source, a longer time is required for heating the film from normal temperature to a high temperature for the third state, resulting in slow response for display. In order to obtain quick response, a large quantity of thermal energy is required instantaneously.
In preparing both a hard copy and a soft copy using a diacetylene derivative film, the hard copy formed on the film utilizing the irreversible change from the first state to the second state is erased when the film is then used for a soft copy utilizing the reversible change between the second state and the third state, because the soft copy is prepared at a higher temperature than the hard copy. For the same reason, the display medium once used for a soft copy can no longer be used for a hard copy. Accordingly, researches have been made on use of diacetylene derivative films to conduct only either hard copy or a soft copy and virtually no attempt has been made for allowing the films to give both a hard copy and a soft copy.
In preparing a hard copy with a film of diacetylene compound, a means for a soft copy has to be separately prepared for the display to confirm preliminarily the information to be written into the hard copy, which will complicate the procedure and the apparatus. Furthermore, it is often desired to take out the necessary information as a hard copy from the soft copy and for this purpose a hard copy means must be provided separately to take out the displayed information as a hard copy, which will also complicate the procedure and the apparatus.